Subagents are specialized Claude instances that run in parallel, each with their own context window and tool access. They're ideal for focused reviews, analysis, or generation tasks.
Note: These are common patterns. Design custom subagents based on the codebase's specific review and analysis needs.
Best for: Automated code quality checks on large codebases
| Recommend When | Detection |
|---|---|
| Large codebase (>500 files) | File count |
| Frequent code changes | Active development |
| Team wants consistent review | Quality focus |
Value: Runs code review in parallel while you continue working Model: sonnet (balanced quality/speed) Tools: Read, Grep, Glob, Bash
Best for: Security-focused code review
| Recommend When | Detection |
|---|---|
| Auth code present | auth/, login, session patterns |
| Payment processing | stripe, payment, billing patterns |
| User data handling | user, profile, pii patterns |
| API keys in code | Environment variable patterns |
Value: Catches OWASP vulnerabilities, auth issues, data exposure Model: sonnet Tools: Read, Grep, Glob (read-only for safety)
Best for: Generating comprehensive test coverage
| Recommend When | Detection |
|---|---|
| Low test coverage | Few test files vs source files |
| Test suite exists | tests/, __tests__/ present |
| Testing framework configured | jest, pytest, vitest in deps |
Value: Generates tests matching project conventions Model: sonnet Tools: Read, Write, Grep, Glob
Best for: API documentation generation
| Recommend When | Detection |
|---|---|
| REST endpoints | Express routes, FastAPI paths |
| GraphQL schema | .graphql files |
| OpenAPI exists | openapi.yaml, swagger.json |
| Undocumented APIs | Routes without docs |
Value: Generates OpenAPI specs, endpoint documentation Model: sonnet Tools: Read, Write, Grep, Glob
Best for: Finding performance bottlenecks
| Recommend When | Detection |
|---|---|
| Database queries | ORM usage, raw SQL |
| High-traffic code | API endpoints, hot paths |
| Performance complaints | User reports slowness |
| Complex algorithms | Nested loops, recursion |
Value: Finds N+1 queries, O(n²) algorithms, memory leaks Model: sonnet Tools: Read, Grep, Glob, Bash
Best for: Frontend accessibility and UX review
| Recommend When | Detection |
|---|---|
| React/Vue/Angular | Frontend framework detected |
| Component library | components/ directory |
| User-facing UI | Not just API project |
Value: Catches accessibility issues, UX problems, responsive design gaps Model: sonnet Tools: Read, Grep, Glob
Best for: Safe dependency updates
| Recommend When | Detection |
|---|---|
| Outdated deps | npm outdated has results |
| Security advisories | npm audit warnings |
| Major version behind | Significant version gaps |
Value: Updates dependencies incrementally with testing Model: sonnet Tools: Read, Write, Bash, Grep
Best for: Framework/version migrations
| Recommend When | Detection |
|---|---|
| Major upgrade needed | Framework version very old |
| Breaking changes coming | Deprecation warnings |
| Refactoring planned | Architectural changes |
Value: Plans and executes migrations incrementally Model: opus (complex reasoning needed) Tools: Read, Write, Grep, Glob, Bash
| If You See | Recommend Subagent |
|---|---|
| Large codebase | code-reviewer |
| Auth/payment code | security-reviewer |
| Few tests | test-writer |
| API routes | api-documenter |
| Database heavy | performance-analyzer |
| Frontend components | ui-reviewer |
| Outdated packages | dependency-updater |
| Old framework version | migration-helper |
Subagents go in .claude/agents/:
.claude/
└── agents/
├── code-reviewer.md
├── security-reviewer.md
└── test-writer.md
| Model | Best For | Trade-off |
|---|---|---|
| haiku | Simple, repetitive checks | Fast, cheap, less thorough |
| sonnet | Most review/analysis tasks | Balanced (recommended default) |
| opus | Complex migrations, architecture | Thorough, slower, more expensive |
| Access Level | Tools | Use Case |
|---|---|---|
| Read-only | Read, Grep, Glob | Reviews, analysis |
| Writing | + Write | Code generation, docs |
| Full | + Bash | Migrations, testing |